return NULL;
if (frequency >= GHZ(1))
r = snprintf(o, 30, "%" PRIu64 " ns", frequency / 1000000000);
else if (frequency >= MHZ(1))
return NULL;
if (frequency >= GHZ(1))
r = snprintf(o, 30, "%" PRIu64 " ns", frequency / 1000000000);
else if (frequency >= MHZ(1))